U.S. Pat. No. 6,501,103 discloses a light emitting diode (LED) assembly comprising an LED (1), a circuit board (2), and a heat-dissipating substrate (3), wherein the LED (1) has a die (12) bound on a heat-dissipating plate (10), and pads electrically connected to a printed circuit board (13). The LED (1) is fixed on the circuit board (2) and the heat-dissipating substrate (3).
The above-mentioned technology generally uses a mechanical method or a soldering method to connect the printed circuit board (13) with the heat-dissipating plate (10). The mechanical method, such as screwing and buckling, needs a large space to install related mechanical devices, and thus is disadvantageous for miniature electronic elements. The soldering method needs to melt solder at a relative high temperature for connecting two different types of materials, wherein the solder temperature is generally higher than 450° C. Usually, the material forming the heat-dissipating plate (10) is metal, such as copper, etc., wherein the thermal expansion coefficient of copper is about 12×10−6/° C. However, the thermal expansion coefficient of the material forming the LED (12) is generally smaller than 10×10−6/° C. or between 4×10−6/° C. and 8×10−6/° C. The difference between the thermal expansion coefficients is likely to cause deformation and fatigue between the LED (12) and the heat-dissipating plate (10) under high temperature, thus reducing the reliability of products containing LED (12) and the heat-dissipating plate (10). In order to reduce the thermal expansion coefficient difference between two materials, the conventional technology adopts a ceramic material of a low thermal expansion coefficient, such as aluminum nitride (AlN), for forming the heat-dissipating plate (10). However, the ceramic material such as AlN is too expensive to be acceptable to market.
In view of the conventional technology's disadvantages, the present invention as described below is provided for achieving effective heat dissipation from the LED, while reducing the negative influence resulted from the difference of the thermal expansion coefficients between different materials.